In 1996, as the tyranny of Dolores Umbridge reached a new level with her becoming Headmistress, the students of Hogwarts revolted en masse, and Dungbombs and Stink Pellets were dropped in the halls with such frequency that it became the new fashion for students to use the Bubble-Head Charm just to ensure that they had a supply of fresh, clean air.[2]

Behind the scenes

Mucus Projectum was a spell planned for the video game adaptation of Harry Potter and the Prisoner of Azkaban, but was cut from the final version of the game. It is possible that the spell would have a similar effect to the manner that Stink Pellets are used in the final game.